50 THE VOYAGE OF H.M.S. CHALLENGER. 



The uropoda (ibid.) are very slender, about equalling in length the three last caudal 

 segments taken together, and are articulated to the last caudal segment somewhat in 

 front of the telson. The scape is narrow, cylindrical, slightly dilated at the end, and 

 reaches to about the tip of the telson ; it exhibits a regular row of about sixteen 

 spinules along the inner edge. The branches are subequal in length and scarcely more 

 than half as long as the scape. The inner branch is composed of three distinctly 

 defined joints, the first of which is a little longer than the other two taken together. 

 All the joints are spinous at the inner edge, the number of spines in the specimen 

 examined amounting to fifteen (eight on the first, four on the second, and three on the 

 last joint) ; to the tip) of the branch, moreover, a somewhat longer spine and a 

 simple bristle are affixed. The outer branch is only biarticulate, wdth the first joint 

 quite short, the last very narrow and gradually tapering, with a few small hair dike 

 bristles along the outer edge, and a somewhat longer seta issuing from the tip. 



Description of the Adult Male. — Whilst the young or not yet sexually mature 

 males do not differ materially in their general appearance from the females, the adult 

 males of this and most other species appear so very dissimilar to the females, as easily to 

 be mistaken for distinct species, a fact that has caused much trouble in the synonymy, 

 several spurious specimens having been introduced on account of this peculiar dissimi- 

 larity between the sexes. 1 



The adult male of the present species attains a much larger size than the female, 

 measuring 21 mm. in length. The form of the body (see PL VI. figs. 3, 4) appears 

 much more slender, the anterior division being far less vaulted and more oblong in 

 shape, and the tail also considerably more elongate. 



The carapace is about twice as long as deep, whereas its height does not nearly 

 equal its breadth; it is consequently much more depressed than in the female, and its 

 dorsal line appears also more evenly curved and less abruptly declining to the base of 

 the pseudorostral projection. The latter is somewhat shorter than in the female, and 

 exhibits above, at the base, a concave space, into the bottom of which the ocular lobe 

 is received. On each side the anterior edges of the carapace form a somewhat projecting, 

 broadly rounded lobe, arching over the base of the antennae. These lobes are serrate at 

 the edge, and, moreover, beset with numerous short plumose bristles (see fig. 4). The 

 inferior edges of the carapace exhibit in the middle a strong, almost angular curvature, 

 and join the posterior margin at an obtuse angle. When viewed from above (fig. 4) 

 the side-edges appear strongly arched, on account of the great development of the 



1 The following is a list of such spurious species : — 



1. Cuma angulata, Kroyer = Adult male of Diastylis rathkii (Kroyer). 



2. Cuma brevirostris, Kroyer = Adult male oi Diastylis edwardsii (Kroyer). 



3. Diastylis spinosa, Norman = Adult male of Diastylis echinata, Spence Bate. 



4. Diastylis stritjata, Norman = Adult male oi Diastylis rugosa, G. 0. Sars. 



5. Diastylis calweri, Norman = Adult male oi Diastylis biplicata, G. 0. Sars. 



